The present invention relates to the field of stationary detection installations, to be arranged on a road in order to detect and, if necessary, record environmental conditions and to monitor and control traffic.
Already in the past it was deemed as necessary to improve road safety inside and outside towns and cities and on motorways by:                monitoring environmental and atmospheric conditions (lighting, mist/fog, ice);        monitoring traffic (number of vehicles traveling in some portions of the road network);        controlling traffic (queues, accidents, obstacles, violations).        
It would be desirable to perform automatically and efficiently said functions, so as to provide users and operators with reliable and real-time information, which allows in particular drivers to modify their driving style (speed, lights on, etc.) or their route (change route or lane) and bodies in charge to modify the concerned installation (lighting, road signs, etc.) and to provide for direct intervention of motorway operators (traffic deviations, aid), as well as to record the scene for after-examination, if required.
In case of fog intermitting emergency lights can be used, with a variable frequency and luminosity, arranged on roads or on traffic dividers. Frequency and intensity of emergency lights, however, should be adjusted depending on outer lighting (day, night, dusk) and visibility conditions so as to obtain an effective signaling and avoid at the same time dazzling phenomena.
The Applicant does not know about prior solutions in the field referred to above, providing for a visual sensor for road applications integrating several functions into its sensitive area.
Conversely, known solutions concern:                sensors for measuring visibility (U.S. Pat. No. 4,931,767, EP0635731B1, GB2224175A, DE19749397, EP0691534, U.S. Pat. No. 5,118,180, U.S. Pat. No. 5,206,698, WO8909015A1, U.S. Pat. No. 5,987,152, DE29811086, U.S. Pat. No. 4,502,782, FR 2745 915)        stationary positions for traffic control (U.S. Pat. No. 5,777,1484, GB2288900, IT MI93A001604, EP1176 570, FR2771363)        